Ecological receptors

PCDDs and PCDEs, together with coplanar PCBs, can express Ah-receptor-mediated toxicity. TCDD (dioxin) is used as a reference compound in the determination of TEFs, which can be used to estimate TEQs (toxic equivalents) for residues of PHAHs found in wildlife samples. Biomarker assays for Ah-receptor-mediated toxicity have been based on the induction of P450 lAl. TEQs measured in field samples have sometimes been related to toxic effects upon individuals and associated ecological effects (e.g., reproductive success). 

When chemicals are released in the environment, their hazard potential to human or ecological receptors depends upon the extent of contact between the receptors and the chemical. This exposure level is not only influenced by where, when and how much of the chemical is released, but also on its movement and changes in air, water, soil or biota relative to the locations of the receptors. Risk is defined as the probability of some adverse consequence in the health context, or as the probability times the extent of the consequence in the technology context. In this paper we shall examine and discuss how mathematical models are used to generate estimates of risk when more than one of the environmental media must be considered in tracing pathways connecting sources with receptors. The principal objective here is to place in perspective the... 

Smith, RN. et al., Preliminary assessment of perchlorate in ecological receptors at the Longhorn Army Ammunition Plant (LHAAP), Karnack, Texas, Ecotoxicology, 10, 305, 2001. 

Ecclesiastical wines, 26 301 Ecdysone receptor agonists, 14 345 ECHIP JMP 4.0.4, features compared to other software, 8 398t ECLP tube press, 11 373 Eco-check Product excellence, 24 189 Eco-efficiency analysis, 24 189, 190 Eco-Efficiency program, 9 457 Ecological and Toxicological Association of Dyestuffs and Organic Pigments Manufacturers (ETAD), 9 234, 238 19 452... 

The receptors of ecological interactions are still not well understood. In fact, many ecological studies have failed to demonstrate well-defined roles for natural products (Pawlik 1993). Most experimental evidence for natural product receptors derives from biomedical applications. Kahalalide F, for example, is a potent cytotoxic depsipeptide (see Sect. 1.3.2.3) initially found in the sacoglossan mollusc Elysia rufescens and later in the green alga it feeds upon (Hamann and Scheuer... 

As indicated above, theoretical models for biological rhythms were first used in ecology to study the oscillations resulting from interactions between populations of predators and preys [6]. Neural rhythms represent another field where such models were used at an early stage The formalism developed by Hodgkin and Huxley [7] stiU forms the core of most models for oscillations of the membrane potential in nerve and cardiac cells [33-35]. Models were subsequently proposed for oscillations that arise at the cellular level from regulation of enzyme, receptor, or gene activity (see Ref. 31 for a detailed fist of references). 

Island would likely become a national wildlife refuge. The cleanup standards, which EPA would establish for each end use scenario, differ in terms of receptors and exposures to inhabitants, which should be defined in an appropriate risk assessment. Receptors are plants, biota, animals, and humans that are exposed to a contaminant of concern. The risk assessment should assess the risks to both human health and ecological receptors, because they may require different end states. PMCD assigned the U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM) to prepare the Conceptual Site Model (CSM) for JACADS closure and to perform the risk assessment. 

From these observations one may wonder whether the ecological role attributed to many natural products is but a shortcut of scientific research, while their fimdamental role remains to be discovered. In any event, the ecological effects played by certain metabolites reflect the variety of receptors and interaction modes in nature. This explains why they may find pharmaceutical use. 

In this chapter it is outlined how man has exploited the signaling, defensive, and environmentally relevant metabolites. That bioactive metabolites of phylogeneticaUy distant organisms are detected by man s receptors finds rationalization in the origin of all organisms fi-om a common ancestor and the limited possibilities of diversification of receptors and biosynthetic pathways. This is why the pharmaceutical industry is interested in chemical ecology (Caporale 1995). 

Bykhovskaia, M. B. and Zhorov, B. S. (1996). Atomic model of the recognition site of the American cockroach pheromone receptor. Journal of Chemical Ecology 22 869-883. 

Conceptual models link anthropogenic activities with stressors and evaluate the relationships among exposure pathways, ecological effects, and ecological receptors. The models also may describe natural processes that influence these relationships. Conceptual models include a set of risk hypotheses that describe predicted relationships between stressor, exposure, and assessment end point response, along with the rationale for their selection. Risk hypotheses are hypotheses in the broad scientific sense they do not necessarily involve statistical testing of null and alternative hypotheses or any particular analytical approach. Risk hypotheses may predict the effects of a stressor, or they may postulate what stressors may have caused observed ecological effects. 

Figure 28.3 The response time and sensitivity of an ecological receptor is a function of the level of biological organization. Higher levels of organization have greater ecosystem relevance. However, as the level of biological organization increases, response time increases, sensitivity decreases, and causal relationships become more uncertain. Ecological risk assessments must balance the need for sensitive, timely, and well-established responses with ecological relevance.

In exposure characterization, credible and relevant data are analyzed to describe the source(s) of stressors, the distribution of stressors in the environment, and the contact or co-occurrence of stressors with ecological receptors. An exposure profile is developed that identifies receptors and exposure pathways, describes the intensity and spatial and temporal extent of exposure, describes the impact of variability and uncertainty on exposure estimates, and presents a conclusion about the likelihood that exposure will occur. 

So far in this section the examples discussed have comprised of hetero aromatic antenna receptors, which mainly function as pH sensors. The detection of metal cations in biological, medical and ecological applications is of major interest. However, this requires more elaborate receptors that can selectively bind a specific metal cation. Naturally, the more elaborate the receptor required, the more challenging its synthesis becomes. The synthesis of lanthanide-based sensors of 53 and 54 has been reported with each ligand incorporating an antenna/receptor selective for zinc(ll) [158,159]. In both cases the receptors are structurally similar, with 53 synthesised from benzylamine and 54 from aniline. 

The receptors of interest included pelagic organisms, benthic organisms and marine mammals (dolphins/porpoises). For the pelagic and benthic organisms, ecological risk assessment was conducted at the population level. For the dolphins and porpoises, risk assessment was conducted at the organism level. 

If the PCDD/PCDF concentrations in soil pose a risk to the environment, remove the ecological receptors from the site—not a feasible action. 2. If the PCDD/PCDF concentrations in soil pose a risk to the environment, remove the soil that is found to be hazardous to ecological receptors. 3. If the PCDD/PCDF concentrations in soil do not pose a risk to the environment, leave the soil at the site. 1. If the NPDES permit limitations are exceeded, the operation of the treatment system continues—not a feasible action. 2. If the NPDES permit limitations are exceeded, the operation of the treatment system is stopped and the GAC vessels are replaced. 3. If the NPDES permit limitations are not exceeded, the operation of the treatment system continues. 

Soil with PCDD/PCDF concentrations that may present a risk to ecological receptors will be removed from the site soil with concentrations that do not present such risk will remain at the site. The operation of the treatment system will proceed uninterrupted until the treated water exceeds the NPDES permit limitations, upon which the operation will stop and the GAC vessels will be replaced. 

An example of a concentration limit is a cleanup level, which is a type of an action level used in remediation projects. Pollutant concentrations in an environmental medium that are greater than the cleanup levels warrant a remedial action. Cleanup levels are often developed based on site conditions, such as future land use exposure pathways the presence of groundwater and the likelihood of its beneficial use the presence of specific ecological receptors background concentrations. 

Since ecological receptors vary from site to site, ecological risk-based concentrations are usually calculated on a project-specific basis. For human receptors, there are... 

Cursory review provides the data user with a limited knowledge of data quality. It is appropriate for the determinations of gross contaminant concentrations for certain project tasks as shown in Table 1. The use of the data that have undergone only a cursory review for making decisions with the consequences for human or ecological receptors would be a serious mistake. 

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